Extender for dye penetrant composition

ABSTRACT

A liquid dye penetrant composition for use in nondestructive testing of objects to locate cracks and other defects or flaws therein, said composition comprising (1) a nonionic surfactant, such as an ocyalkylated aliphatic alcohol, (2) a small amount of a dye soluble in the surfactant and (3) a substantial and preferably a major proportion, of a high boiling narrow-cut isoparaffinic solvent consisting essentially of a mixture of isoparaffins having a chain length of about 10 to about 17 carbon atoms, and an average chain length of about 13 to about 14 carbon atoms, as extender. Such composition is applied to the surface of an object containing cracks and other defects, water is applied to the surface of the object to remove excess liquid dye penetrant composition from the surface without removing such penetrant from such cracks and other defects, and with or without a developer, the surface of the object is viewed under suitable lighting conditions, e.g. ultraviolet or black light when the dye in the penetrant is a fluorescent dye, to locate any cracks or other defects in the surface of the body as indicated by colored traces from the dye penetrant remaining in such cracks and other defects.

BACKGROUND OF THE INVENTION

This invention relates to an improved dye penetrant composition andmethod for non-destructively testing materials to locate defects open tothe surface, such as cracks, and is more particularly concerned with theprovision of an extender which is compatible with the liquid vehicle ofthe dye penetrant, and is compatible with the metals or alloys,particularly titanium and nickel alloys, of which the objects beingtested are comprised, as well as possessing other importantcharacteristics such as low viscosity, low volatility, quick penetrationinto cracks and voids, and low toxicity.

In known penetrant inspection methods for rapid location and evaluationof surface flaws such as cracks in test bodies or parts, a dye penetrantcomposition, preferably containing a fluorescent dye, and which willpenetrate the openings of the surface of cracks or other voids in thepart, is applied to the surface of the test body, and the excesspenetrant composition is removed from the surface of the body. Adeveloper composition may then be applied to the part surface, whichacts as a wick and causes the liquid penetrant containing thefluorescent dye, which was retained in the cracks, to be drawn up out ofthe surface defects by capillary action. The part is then exposed toappropriate lighting conditions such as invisible fluorescigenous light,and the location of the surface cracks is revealed by the emission ofvisible fluorescent light by the penetrant dye which was retained in thecracks after the penetrant composition was removed from the surface ofthe part.

For best efficiency, particularly for the detection and location ofminute surface cracks, as well as intermediate size and gross cracks, itis necessary that the dye penetrant composition have high sensitivity.

Volatile type solvents are commonly employed for extending or thinningdye penetrant inspection solutions or compositions. This is done chieflyfor the purpose of lowering the viscosity of the penetrant in order toadapt it for application in spraying systems. Thus for example solventssuch as kerosene, light fuel oils, light mineral oil, mineral thinnerand methyl ethyl ketone, all highly volatile solvents, have heretoforebeen employed in prior art dye penetrants. See for example U.S. Pat.Nos. 2,806,959 and 3,429,826. Further, most dye penetrant solutions inpractice generally require the use of a combination of solvents,including primary and secondary solvents, extender solvents and wettingagents.

Further, with the advent of new alloys employed in aircraftconstruction, such as titanium and nickel alloys, considerable efforthas been made in selecting solvents which can be compatible with suchalloys. Solvents compatible with these alloys generally are selectedbecause of their unusually low chloride content and low sulfur content.

Accordingly, an object of the present invention is the provision of animproved dye penetrant composition containing an extender which has anumber of unique advantages over extenders previously employed in dyepenetrant compositions. A particular object of the invention is theprovision of a novel dye penetrant composition containing an extenderwhich is relatively inexpensive and which is compatible with certain dyepenetrant composition vehicles and with certain alloys used in aircraftconstruction such as titanium and nickel alloys, and particularlyaffording a dye penetrant composition of low viscosity, low toxocity andwhich is substantially odorless. A further object is to provideprocedure for dye penetrant inspection of objects, utilizing such dyepenetrant composition.

SUMMARY OF THE INVENTION

The above objects and advantages are achieved according to the inventionby employing as an extender for a dye penetrant composition containing anonionic surfactant vehicle and a dye soluble therein, an isoparaffinicsolvent consisting essentially of isoparaffins and having certain uniquephysical and chemical characteristics, as defined below. Arepresentative extender of this type is marketed as "Isopar M" by Exxon.

The isoparaffinic solvent extender is particularly effective inconjunction with nonionic surfactants employed as vehicle for the dye inthe dye penetrant compositions hereof. The isoparaffinic solventextender employed herein has a number of advantageous propertiesincluding low viscosity, high flash point, low toxicity and absence ofodor. In addition, the dye penetrants obtained by employing theisoparaffinic extender hereof have the ability to quickly penetratecracks and flaws, including microcracks, and have a "self-developing"action, as described in greater detail hereinafter.

The liquid dye penetrant compositions hereof including the uniqueextender can be formulated as a water washable or solvent removeable dyepenetrant composition containing a nonionic water soluble surfactant, oras a post emulsifiable dye penetrant composition containing a nonionicsurfactant of relatively low solubility. In the latter case, followingapplication of the dye penetrant composition to the surface of an objectto be inspected, an emulsifier composition is then applied to thesurface, the emulsified penetrant composition is then removed as byspraying with water, and the surface inspected under suitable light toobtain the desired indications of cracks and other flaws in the partsurface.

Accordingly, there is provided according to the invention a liquid dyepenetrant composition for use in non-destructive testing for detectingcracks and other flaws in the surface of an object, comprising (1) anonionic surfactant, (2) a small amount of a dye soluble in saidsurfactant and (3) as extender, a substantial portion of a high boilingnarrow-cut isoparaffinic solvent consisting essentially of isoparaffins,as defined more specifically hereinafter, an illustrative preferredextender of this type having a high flash point of about 175° F. and ahigh autoignition temperature of about 730° F.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The nonionic surfactant or carrier, and which is employed essentially asthe sole vehicle for the dye of the dye penetrant compositions accordingto the invention, includes any preferably water soluble nonionicsurfactants of low viscosity, which are compatible with theisoparaffinic solvent extender and the dye dissolved in the surfactantvehicle, and which are compatible with metals, particularly thoseemployed in the aircraft industry, including titanium and nickel alloys.Such nonionic surfactant must be capable of penetrating minute cracksand other defects in the surface of an object, to carry a film of dyepenetrant composition into such cracks and other surface defects, so asto reveal such cracks and other defects due to the dye contained in thecomposition.

Suitable nonionic surfactant vehicles for the dye penetrant compositionsof the invention include oxyalkylated aliphatic alcohols, alkoxylatedalkyl phenols and alkyl aryl polyether alcohols, and mixtures thereof.Thus, a preferred class of nonionic surfactants employed in the dyepenetrant compositions of the invention are the oxyalkylated aliphaticalcohols which can be prepared by the reaction of an organic compoundhaving a reactive hydrogen atom, such as an aliphatic alcohol, withethylene oxide, propylene oxide, or mixtures thereof. Such surfactantsare biodegradable.

Thus, the latter preferred class of nonionic surfactants consistessentially of an oxyalkylated aliphatic alcohol or mixtures thereof,formed of an aliphatic primary or secondary alcohol carrying ethoxy orpropoxy groups, including polyoxyethylene or polyoxypropylene groups, ormixtures thereof.

More particularly, one class of such nonionic solvents or carriers canbe defined as straight chain, primary, aliphatic oxyalkylated alcohols,generally in the form of mixtures thereof, wherein the primary aliphaticalcohols can have from 8 to 20 carbon atoms, preferably 10 to 18 carbonatoms, and the oxyalkyl groups are ethylene oxide and propylene oxide,preferably in the form of a mixture thereof.

One group of nonionic carriers within the class of materials definedimmediately above is a cogeneric mixture of compounds represented by theformula:

    R--O(A)H                                                   (1)

wherein:

R is an essentially linear alkyl group having from 10 to 18 carbonatoms, with the priviso that at least 70 weight percent of saidcompounds in said mixture have an R of from 12 to 16 carbon atoms, and Ais a mixture of oxypropylene and oxyethylene groups, said oxypropyleneand oxyethylene groups being from 55% to 80% of the total weight of thecompounds, the oxypropylene to oxyethylene ratio of said total weightbeing from 0.85:1 to 2.75:1, preferably 1.25:1 to 2.25:1.

Another preferred class of condensation products or oxyalkylatedalcohols within the above definition are those wherein the aliphaticalcohols of the oxyalkylated alcohols, or R in the above formula, rangesfrom 12 to 18 carbon atoms, and the total number of ethylene oxide andpropylene oxide groups in the mixture thereof, or designated A in theabove formula, ranges from about 4 to about 14.

The term "cogeneric mixture" as employed herein, designates a series ofclosely related homologues obtained by condensing a plurality of oxideunits, with an alcohol or a mixture thereof. As is known, when a mixtureof this type is generated, various oxyalkylene chain lengths areobtained.

Alcohols which may be employed in the preparation of the products notedabove are those essentially linear, primary, aliphatic alcohols havingfrom 8 to 20 carbon atoms, preferably 10 to 18 carbon atoms. Mixtures ofalcohols are usually preferred since their use provides for a goodbalance of properties in the resulting products. Examples of alcoholswhich are operable include decyl alcohol, undecyl alcohol, laurylalcohol, tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, cetylalcohol, heptadecyl alcohol, stearyl alcohol, hydrogenated tallowalcohol, and mixtures thereof. They may be naturally-derived such asfrom coconut oil or synthetically-derived such as from linear alkanes orlinear olefins.

The above nonionic surfactants employed as carrier or vehicle for thedye of the penetrant solution according to the invention, are preparedby condensing an alcohol or mixture of alcohols, as described above,with a mixture of ethylene oxide and propylene oxide, in the presence ofan alkaline catalyst, such as potassium hydroxide. The oxide mixture maybe added to the alcohol in one continuous step or it may be added inseveral steps. The products thus produced possess random distribution ofoxyethylene and oxypropylene groups.

The nonionic surface active agents described above and their method ofpreparation are disclosed in U.S. Pat. No. 3,504,041, and suchdisclosure is incorporated herein by reference. These surface activeagents are believed to include for example, that class of surfactantswhich are marketed as the "Plurafac" surfactants "RA-40" grades.

Another class of biodegradable liquid, water miscible oxyalkylatedalcohol condensation products within the above definition are thosewherein the aliphatic alcohol, or R, is a straight chain alkyl grouphaving from 8 to 20 carbon atoms, the number of ethylene oxide groups inthe mixture thereof with propylene oxide, or A, ranges from 3.75 to12,75, and the number of propylene oxide groups in such mixture rangesfrom 1.7 to 7.0, the oxyethylene to oxypropylene ratio in such mixturesbeing from 1.8:1 to 2.2:1. This mixture of condensation products and themethod of their preparation are disclosed in U.S. Pat. No. 3,340,309,and such disclosure is also incorporated herein by reference. Thenonionic oxyalkylated alcohols marketed as the "R0-20" grades of"Plurafac", are believed representative of the class of surface activeagents disclosed in the latter patent.

Various other "Plurafac" grades which are marketed and are believed tobe generally within the above-described classes of oxyalkylated alcoholsurfactants are those designated RA-43, A-24, A-25, B-25-5, B-26 andD-25.

Dye penetrant compositions containing the above described primaryaliphatic oxyalkylated alcohols as vehicle, and a dye are described inmy U.S. Pat. No. 3,915,885.

A class of particularly preferred nonionic biodegradable solvents orcarriers which can be employed as substantially the sole vehicle for thedye of the dye penetrant compositions according to the present inventionare ethoxylates of a mixture of linear secondary aliphatic alcohols,with the hydroxyl groups randomly distributed, the linear aliphatichydrophobic portion of such alcohols being a mixture of alkyl chainscontaining in the range from 10 to 17 carbon atoms, preferably from 11to 15 carbon atoms, and containing an average of from 3 to 12 moles ofethylene oxide.

The above particularly preferred class of nonionic biodegradablesurfactant employed as carrier for the dye penetrant of the invention isa mixture of compounds which can be represented by the formula: ##STR1##where n is in the range from 9 to 13, and m is 3 to 12.

Although preferably each of the above-defined surfactants is formed of amixture of two or more linear alkyl hydrophobic chains ranging from C₁₁to C₁₅, as noted below, the surfactant can contain a single such chainformed from a single secondary aliphatic alcohol of the types describedbelow.

The linear alkyl hydrophobic portion of the above defined surfactant isa mixture of C₁₁ to C₁₅ linear alkyl chains, and can be derived from amixture of C₁₁ to C₁₅ aliphatic secondary alcohols, for example thesecondary undecyl, dodecyl, tridecyl, tetradecyl and pentadecylalcohols. The hydrophilic portion of the surfactant is a polyoxyethylenechain randomly attached to any carbon atom of the linear alkylhydrophobic chains, other than to the terminal carbon atoms thereof,through an ether linkage. It will accordingly be understood that thespecific carbon atom in the alkyl hydrophobic chains to which thehydrophilic polyoxyethylene chain is attached will become a ##STR2##Such hydrophilic polyoxyethylene chain is generally expressed in termsof an average number of moles of ethylene oxide.

Illustrative examples of biodegradable nonionic surfactants of the typesdefined in the above formula are those consisting of a mixture ofethoxylates of from 11 to 15 carbon atoms in the aliphatic hydrophobicchain, and which have an average of 3, 5, 7, 9 and 12 moles of ethyleneoxide, respectively, as the hydrophil.

Materials corresponding to these five examples of biodegradable nonionicsurfactants are marketed, respectively, as:

Tergitol 15-S-3

Tergitol 15-S-5

Tergitol 15-S-7

Tergitol 15-S-9

Tergitol 15-S-12

In each case of the Tergitol S series of surfactants listed above, thenumber to the left of the "S" indicates a hydrophobic aliphatic chain offrom 11 to 15 carbon atoms derived from a mixture of alcohols on C₁₁ toC₁₅ backbone chains, and the number to the right of the "S" designatesthe average number of moles of ethylene oxide as the hydrophil. Thus forexample, Tergitol 15-S-5 is a mixture of linear aliphatic alcohols inthe C₁₁ to C₁₅ range ethoxylated with an average of 5 moles of ethyleneoxide. All of these commercially marketed Tergitol S series ofsurfactants are water soluble except for Tergitol 15-S-3, which isessentially water insoluble. Mixtures of these materials can also beemployed in providing the dye penetrant of the invention, such as amixture of the above Tergitols 15-S-5 and 15-S-3; a mixture of 15-S-3and 15-S-9; and a mixture of 15-S-5 and 15-S-9.

The above preferred class of nonionic biodegradable surfactants employedas carrier or vehicle for the dye of the penetrant solution according tothe invention, are prepared by reacting an alcohol or mixture ofalcohols, with the desired proportion of ethylene oxide, in the presenceof an alkaline catalyst, such as potassium hydroxide. The ethylene oxidemay be added to the alcohol or mixture or alcohols in one continuousstep or it may be added in several steps. The products thus producedpossess random distribution of oxyethylene groups, as noted above.

Another process for preparing the above nonionic surfactants in the formof ethoxylates of linear secondary aliphatic alcohols, is described inU.S. Pat. No. 2,870,220.

Although Tergitol 15-S-3 is essentially water insoluble and is usuallyemployed in combination with the other members of the Tergitol S seriesnoted above, such as Tergitol 15-S-5, dye penetrant compositionsaccording to the invention containing Tergitol 15-S-3 alone, can beemployed. However, Tergitol 15-S-3 has its greatest utility forproduction of dye penetrants having high sensitivity according to theinvention, when employed in combination with the other water washableand water soluble Tergitols such as Tergitol 15-S-5 and Tergitol 15-S-9.

Dye penetrant compositions containing the above described ethoxylates ofsecondary aliphatic alcohols as vehicle and a dye are described in myU.S. Pat. No. 3,915,886.

Also, particularly effective dye penetrants are provided according tothe invention employing a combination or mixture of the above Tergitols15-S-5 and 15-S-9, and to which there can be added optionally Tergitol15-S-3, as described in my U.S. Pat. No. 3,939,092.

There can also be employed ethoxylates of linear primary alcohols,corresponding to the ethoxylates of the linear secondary alcohols of theTergitol S series of nonionic surfactants described above. Thus, theTergitol 25-L series of nonionic surfactants is derived by ethoxylationof a blend of C₁₂ to C₁₅ linear primary alcohols, the solublederivatives of which contain from about 5 to about 7 moles of ethyleneoxide.

Other nonionic surfactants which can be employed include alkyl phenols,particularly alkoxylated alkyl phenols such as ethoxylated alkylphenols, e.g. ethoxylated octyl- or nonyl phenol containing from about 7to about 15 moles of ethylene oxide per mole of alkyl phenol, which arewater soluble. The water insoluble derivatives of such ethoxylated alkylphenols containing up to 5 moles of ethylene oxide per mole of alkylphenol can be employed in post emulsifiable isoparaffinic solventextended dye penetrants of the invention, described in greater detailhereinafter. Also, alkyl aryl polyether alcohols can be employed such asthe material marketed as "Triton X-100," which is isooctyl phenylpolyethoxy ethanol.

The extender incorporated into the dye penetrant composition of theinvention containing a nonionic surfactant of the types exemplifiedabove, is an isoparaffinic solvent. The isoparaffinic solvent consistsof an isoparaffin having a carbon chain ranging from about 10 to about17 carbon atoms, and preferably consists essentially entirely of amixture of isoparaffins having carbon chains ranging from about 10 toabout 17 carbon atoms and an average carbon chain ranging from about 12to about 15, preferably about 13 to about 14, carbon atoms. Thus, theisoparaffinic solvent is practically about 100% of the above isoparaffinor mixture of isoparaffins, and which may contain only a very smallamount, e.g. of the order of about 0.1%, normal paraffins. Suchisoparaffinic solvent has a number of unique characteristics includinglow viscosity of the dye penetrants produced therewith, a high flashpoint, exceptionally high autoignition temperature, very low volatilityand absence of odor. Another unique characteristic of the isoparaffinicsolvent extender of the invention is that it provides a quickpenetration of cracks and other surface defects and a "creeping" orself-developing action in dye penetrants containing such solvent. By"creeping" or "self-developing action" is meant that the dye penetrantwhich penetrates into the cracks and other defects tends to exudetherefrom without the aid of a developer, to provide colored indicationsof such cracks and other defects.

A representative preferred isoparaffinic solvent particularly having theabove chemical and physical characteristics is the solvent marketed as"Isopar M" by Exxon. This solvent is a high boiling narrow-cutisoparaffinic solvent of high purity, having a high flash point of about175° F. (ASTM D 93), and high autoignition temperature of about 730° F.(ASTM D 286). Such solvent is an isoparaffinic material consisting of amixture of isoparaffins as above defined, having an average of about131/2 carbon atoms in the isoparaffinic chain, and an average molecularweight of 191, a specific gravity at 60° F. of 0.784, a viscosity at 25°C. of 3.35 cs (ASTM D 445) and a refractive index at 20° C. of 1.4362(ASTM D 1218). The solvent also has low toxicity including a very lowlevel of skin irritants and a very low concentration, limited to a fewppm, of trace impurities such as sulfur, chlorine, acids, and carbonyls.

Any suitable dye generally employed in dye penetrant compositions can beincorporated into the nonionic surfactants described above for producingthe dye penetrant compositions employed in the invention process.Preferably, however, a fluorescent dye is employed for this purpose. Thenonionic surfactant vehicle for the dye is compatible therewith and hasthe ability to dissolve either small or relatively large amounts of thedye and to hold a high concentration of dye in solution while providinggood resolution and clarity of the dye trace in the cracks and othersurface defects.

As previously noted, the dye penetrant solution employed according tothe invention preferably contains a fluorescent dye. Various types offluorescent dyes can be employed including for example the dye marketedas Fluorol 7GA and Morton Fluorescent Yellow G, as well as otherfluorescent dyes such as those marketed as Calcofluor Yellow, AzosolBrilliant Yellow 6GF; Rhodanine B, Rhodanine 6 GDN, Calcofluor White RW,Blancophor White AW, Auramine and Eosine G, and water solublefluorescent dyes such as Blancophor FFG.

The dye penetrant composition employed according to the inventionalternatively can contain non-fluorescent or daylight type dyes such asazo type dyes, e.g. xyleneazo-beta-naphthol, Mefford No. 322 dye,believed to be o-toluene-azoxyleneazo-beta-naphthol, and the azo dyesmarketed as Oil Red "0" and Sudan Red. These dyes conveniently can beemployed where daylight or white light is only available, andparticularly where the surface of the body to be detected containsrelatively gross cracks. However, it is preferred to employ fluorescentdyes having greater sensitivity or detectability as result of the highcontrast obtained by the fluorescent indications.

The amount of dye which is incorporated into the nonionic, e.g.oxyalkylated alcohol, surfactant or carrier to produce the dye penetrantcomposition of the invention, can range from about 0.1 to 15, preferablyabout 0.5 to about 10, parts of the dye, or mixtures thereof, per 100parts of such nonionic surfactant, by weight. In preparing the dyepenetrant composition employed according to the invention, the dye issimply added to the nonionic surfactant carrier, in the desiredproportion. The resulting dye penetrant composition has both high andlow temperature stability.

The amount of isoparaffinic solvent extender added to the dye penetrantconstitutes a substantial, and usually a major proportion, of theresulting solution, such solvent preferably being present in at leastequal volumetric proportions with respect to the nonionic surfactant.Generally, the dye penetrant including the above nonionic surfactant anddye, is diluted with such solvent in a proportion ranging from about 0.5to about 15, preferably about 1 to about 7, parts of the isoparaffinicsolvent to 1 part of dye penetrant, consisting of the sum of the othercomponents, that is nonionic surfactant or surfactants, and dye, byvolume.

Typical dye penetrant compositions to which the isoparaffinic solventcan be added according to the invention are as follows:

                                      TABLE 1                                     __________________________________________________________________________    Compositions (Parts by Weight)                                                COMPONENTS A  B  C  D   E   F  G  H                                           __________________________________________________________________________    Tergitol 15-S-5                                                                          75 75 50 100 --  75 75 75                                          Tergitol 15-S-9                                                                          25 25 -- --  100 .25                                                                              25 25                                          Tergitol 15-S-3                                                                          -- -- 50 --  --  -- -- --                                          Plurafac A-24                                                                            -- -- -- --  --  -- -- --                                          Calcofluor White RW                                                                       5 2.5                                                                               5  5  2.5 1.5                                                                               .75                                                                              .375                                       Fluorol 7 G A                                                                            1.5                                                                               0.75                                                                            1.5                                                                              1.5  .75                                                                              -- -- --                                          Morton Fluorescent                                                                       -- -- -- --  --  0.5                                                                              0.25                                                                             0.125                                       Yellow G                                                                      __________________________________________________________________________

As the volume of isoparaffinic solvent incorporated into the dyepenetrant composition increases in relation to the nonionic surfactantand dye concentration, the level of dye penetrant sensitivity decreases,that is from high sensitivity employing a relatively low volume ofisoparaffinic solvent, to low sensitivity employing a relatively highvolume of isoparaffinic solvent. The isoparaffinic solvent can beintroduced into the dye penetrant formulation at essentially any stageduring the mixing and formulation of the dye penetrant.

Illustrative examples incorporating varying proportions of theisoparaffinic "Isopar M" solvent into the typical dye penetrantcomposition F of Table 1 above, and the sensitivity level of theresulting respective compositions, are set forth in Table 2 below.

                                      TABLE 2                                     __________________________________________________________________________    Low-Viscosity Fluorescent Water Washable Penetrants                                     DYE PENETRANT       Approximate level of                            DILUTED   Composition F                                                                           "Isopar M" Solvent                                                                      Penetrant Sensitivity                           COMPOSITIONS                                                                            (Parts by Volume)                                                                       (Parts by Volume)                                                                       Obtained                                        __________________________________________________________________________    I         1         1         High Sensitivity                                II        1         3         Medium Sensitivity                              III       1         7         Low Sensitivity                                 __________________________________________________________________________

The metal surfaces to which the dye penetrant compositions can beapplied include a wide variety of metals and alloys and particularlythose generally used in the aircraft industry, such as aluminum, copper,titanium, nickel, and their alloys, e.g. chromium plated brass, steelalloys such as PH14-8 Mo, the stainless series of steels, and the like.

If desired, a developer composition can be employed in conjunction withthe isoparaffinic solvent containing dye penetrant composition of theinvention. When employed, a dry powder or non-aqueous (volatile solventbase) developer composition can be utilized. In each case, the developercomposition contains a light colored powder, forming a coating whichcontrasts with the color of the dye in the penetrant and which acts as awick or blotter, and causes liquid penetrant containing the dye, e.g.fluorescent dye, which was retained in the cracks or other surfaceflaws, to be drawn up out of such surface defects by capillary actionand to "bleed" through the powder. Exemplary developer compositions foruse in conjunction with the dye penetrant composition according to theinvention, are those described in my U.S. Pat. No. 4,069,419, which is adry powder developer consisting of fumed silica and talc, and in my U.S.Pat. No. 3,748,469, which is a wet nonaqueous developer compositionconsisting essentially of isopropyl alcohol, talc and glycol monobutylether. The description of such developer compositions contained in theabove patents are incorporated herein by reference.

The dye penetrant composition employed in the invention process,utilizing the above nonionic, e.g. oxyalkylated alcohol, surfactants canbe tailored to have varying degrees of sensitivity for detection of thesmallest microcracks to gross cracks in a part surface by generallyvarying the amount of dye incorporated, and also by selecting particularsurfactants or combinations thereof.

In the method for detecting cracks and other flaws in the surface of anobject employing the isoparaffinic solvent extended dye penetrantcomposition of the invention, such dye penetrant is applied to the partsurface in any suitable manner, as by spraying. The low viscositysolvent extended penetrant quickly penetrates surface defects such asthe cracks in the part surface, and immediately after application of thedye penetrant to the surface of the test part, the excess dye penetrantcomposition is readily removed from the object surface by water washing,e.g. by application of a water spray or a sprayed mixture of air andwater, or by wiping with a water moistened cloth. The solvent extendeddye penetrant compositions hereof, particularly these containing theabove Tergitols 15-S-5 to 15-S-9, generally have excellent wetabilityand practically instantaneous washability with water without removingdye penetrant from the cracks and defects on the part surface, followedby drying the part surface. Such dye penetrant compositions can also beremoved from the part surface by means, for example, of an organicsolvent such as an alcohol, e.g. isopropyl alcohol, a ketone such asacetone, or a chlorinated hydrocarbon such as trichlorethane.

As previously noted, the isoparaffinic solvent extended dye penetrant ofthe invention has a self-developing action, in that such dye penetrant"creeps" or exudes from the cracks without the aid of a developer, toprovide indications of the cracks when the part is thereafter viewedunder suitable light, e.g. fluorescent light when the penetrant containsa fluorescent dye.

If desired, however, following removal of excess penetrant, a developercomposition, e.g. of the types noted above, can then be applied to thepart surface followed by removal of excess developer, as by means of anair blast. The part is then viewed under suitable lighting conditions,employing black light or fluorescent illumination when the dye penetrantcontains a fluorescent dye.

Where it is desired to employ a relatively insoluble nonionic surfactantin the dye penetrant composition, such as Tergitol 15-S-3 noted above,alone or in substantial proportion in admixture with another watersoluble Tergitol such as Tergitol 15-S-5, in order to obtain highsensitivity, the post emulsifiable dye penetrant inspection method of myU.S. Pat. No. 3,981,185 can be employed. According to such procedure,the dye penetrant composition containing the nonionic surfactant, e.g.the oxyalkylated alcohol nonionic surfactant, such as Tergitol 15-S-3 ascarrier, and diluted with the isoparaffinic solvent according to theinvention, can be applied as by dipping or spraying, preferably thelatter to a test part, and the solvent evaporated, e.g. in about 1 to 5seconds, followed by treatment of the penetrant covered part as byspraying, with an emulsifier containing as an essential component watersoluble nonionic surfactants, e.g. nonionic surfactants of the samegeneral class as employed as carrier for the dye in the dye penetrantcomposition, but having greater water solubility, such as Tergitol15-S-9, or a combination of Tergitols 15-S-3 and 15-S-12. Water also canbe added to the emulsifier. In such postemulsifiable process, the dyepenetrant can contain an oxyalkylated alcohol nonionic surfactantaccording to formula (2) above, having an average value for m in suchformula of about 3 to 4, and the oxyalkylated alcohol nonionicsurfactant in the emulsifier can have an average value for m of about 5to 12.

After a dwell time of about 1 to 5 minutes, the resulting emulsifiedpenetrant is then removed from the surface of the part as by sprayingwith water, without dislodging the dye penetrant from the surface cracksand thus entrapping the penetrant therein, and the part surface is thendried and inspected under suitable light, e.g. ultraviolet light. Ifdesired, a developer also can be employed following removal of theemulsified penetrant from the part surface.

The following is an example of a typical basic post emulsifiable dyepenetrant composition having high sensitivity.

                  TABLE 3                                                         ______________________________________                                        Composition J                                                                 Components            Parts by weight                                         ______________________________________                                        Tergitol 15-S-3       100                                                     Calcofluor White RW   1.5                                                     Morton Fluorescent Yellow G                                                                         0.5                                                     ______________________________________                                    

Illustrative examples of post emulsifiable low viscosity fluorescent dyepenetrants containing varying amounts of isoparaffinic solvent are setforth in Table 4 below.

                                      TABLE 4                                     __________________________________________________________________________    Low Viscosity Fluorescent Post Emulsifiable Penetrants                                  DYE PENETRANT                                                                           Exxon     Approximate level of                            DILUTED   COMPOSITION J                                                                           "Isopar M" Solvent                                                                      Penetrant Sensitivity                           COMPOSITION                                                                             (Parts by Volume)                                                                       (Parts by Volume)                                                                       Obtained                                        __________________________________________________________________________    IV        1         1         High Sensitivity                                V         1         3         Medium Sensitivity                              VI        1         7         Low Sensitivity                                 __________________________________________________________________________

The above isoparaffinic solvent diluted penetrant compositions IV, V andVI of Table 4 can be employed in conjunction with a subsequentemulsifier solution such as illustrated in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        COMPOSITION K                                                                 Components         Parts by Volume                                            ______________________________________                                        Tergitol 15-S-3    15                                                         Tergitol 15-S-12   50                                                         Water Distilled    390                                                        ______________________________________                                    

If desired, a small amount of dye such as Rhodanine can be used to colorthe emulsifier in order to impart visibility to the solution.

The following are examples of practice of the invention.

EXAMPLE 1

The low viscosity diluted isoparaffinic solvent extended composition Iof Table 2 above was applied as by spraying, to one-half of the surfaceof a cracked aluminum test panel containing minute cracks of the orderof 0.001" to 0.0001" in width, closely distributed over the entiresurface. A water wash was then applied as by an air-water spray over thecoating of the dye penetrant composition I on the test panel, causinginstantaneous washing away of the dye penetrant on the surface of thepanel without dislodging the dye penetrant from the surface cracks andthus entrapping the penetrant therein.

The other half of the test panel surface was sprayed with the undiluteddye penetrant composition F of Table 1 above, and which was the basiccomposition employed in producing the diluted isoparaffinicsolvent-containing dye penetrant composition I of the invention, andutilized on the first half of the test panel. A water wash was thenapplied by an air-water spray over the coating of dye penetrantcomposition F to wash away excess dye penetrant from the surface of thepanel.

Both halves of the test panel surface to which the diluted dye penetrantcomposition I above and dye penetrant composition F were initiallyrespectively applied, were then covered with the powder developer below,disclosed in my U.S. Pat. No. 4,069,419.

                  TABLE 6                                                         ______________________________________                                        Components          % by weight                                               ______________________________________                                        Talc                50                                                        Fumed Silica        50                                                        ______________________________________                                    

The above developer was permitted to dwell over the two half surfaces ofthe test panel for a period of about 2 minutes.

Excess developer composition was then carefully removed from both halfsurfaces of the test panel by means of a gentle air blast.

The panel was then placed under black light (fluorescent) illuminationand the respective half surfaces viewed in such illumination. It wasobserved that the first half side of the panel which was initiallytreated with diluted dye penetrant composition I according to theinvention, disclosed fluorescent indications from numerous readilydefined microcracks, which fluorescent indications were substantially ofthe same brightness and concentration as those fluorescent indicationsfrom the microcracks on the half side of the panel which had beeninitially treated with the basic penetrant composition F.

EXAMPLE 2

The procedure of Example 1 is followed except that in place of thepowder developer employed in Example 1, a nonaqueous developer havingthe following composition, according to my U.S. Pat. No. 3,748,469 isemployed:

                  TABLE 7                                                         ______________________________________                                        Components            % by weight                                             ______________________________________                                        Isopropyl alcohol     70.5                                                    Talc                  28.6                                                    Glycol monobutyl ether                                                                              0.9                                                     ______________________________________                                    

The above developer is permitted to remain on the panel surface to whichit is applied for a period of 2 minutes, until substantially all of theisopropyl alcohol evaporates and substantially dry powder coating forms.

Results similar to the results of Example 1 are obtained.

EXAMPLE 3

Tests on aluminum panels containing microcracks were carried outemploying procedures similar to that employed in Example 1, utilizingcomposition II of Table 2, the medium sensitivity low viscosity dilutedfluorescent dye penetrant composition of the invention, on one-half ofthe surface of the test panel and utilizing the basic medium sensitivityundiluted basic composition G of Table 1 on the other half of the panel.

Results obtained were similar to those obtained in Example 1, exceptthat in both cases the sensitivity and concentration of cracks revealedwere not as great as for the high sensitivity dye penetrant compositionsI and F of Example 1.

EXAMPLE 4

The high sensitivity low viscosity post emulsifiable penetrantcomposition IV of Table 4 above was applied as by spraying to one-halfof the surface of an aluminum test panel containing microcracks.

The other half of the test panel surface was sprayed with the undilutedhigh sensitivity post emulsifiable dye penetrant composition J of Table3.

The dye penetrant covered surfaces on both halves of the test panel werethen sprayed with the emulsifier solution composition K of Table 5above, the emulsifier being allowed to dwell on the initially appliedpenetrant for about 2 minutes, and thereafter a spray of water was usedto remove the emulsifier-penetrant blend on each half of the panel.

Both halves of the test panel were then covered with the powderdeveloper of Table 6 above and excess developer composition was thenremoved from both surfaces of the test panel by means of a gentle airblast.

The panel was then placed under black light (fluorescent) illuminationand the above treated surfaces on both halves of the panel viewed insuch illumination. The sharpness and brilliance of the fluorescentindications on the first half of the panel to which the isoparaffinicsolvent diluted post emulsifiable penetrant was applied weresubstantially the same as for the other half of the panel to which theundiluted post emulsifiable penetrant was applied.

EXAMPLE 5

The procedure of Example 1 was followed except that the first half ofthe panel was treated initially with a low viscosity red visible waterwashable dye penetrant composition VII consisting of 3 parts Tergitol15-S-9 surfactant, 2 parts Oil Red "O" dye and 8 parts "Isopar M"solvent, by volume, and the other half of the panel was treated with thesame dye penetrant composition but which was not diluted with the"Isopar M" solvent.

Both halves of the test panel, following developing according to Example1, were viewed in visible light, revealing visual colored traces ofcrack indications on both sides of the panel of approximately equalbrightness and intensity.

Prior to applying the developer in the tests of all of the aboveexamples, observations were made on the half portions of the test panelscovered with the three types of low viscosity solvent extended dyepenetrants of the invention, namely, the low viscosity fluorescent waterwashable penetrant composition I of Table 2, the low viscosityfluorescent post emulsifiable penetrant composition IV of Table 4, andthe low viscosity red visible water washable penetrant of Example 5, tojudge their self-developing action produced by utilizing the "Isopar M"solvent. In all cases these penetrants appeared to have remarkableself-developing action in that the dye penetrant appeared to commenceexuding from the cracks shortly after removal of excess dye penetrantfrom the part surfaces. This unique property of the dye penetrantobtained using the isoparaffinic solvent of the invention appearsrelated to the low viscosity and quick penetration of the resulting dyepenetrant into the surface cracks. The low viscosity of the dyepenetrant also results in reduced drag-out action, namely, the abilityof the dye penetrant to readily drip from the part. Thus, when carryingout the dye penetrant process employing a dye penetrant tank, as bydipping the parts in the tank, such quick drainage of excess dyepenetrant from the part when it is removed from the tank permitsrecovery of excess penetrant and thus increases the economy of thesystem.

The excess of both the isoparaffinic solvent extended water washable dyepenetrants of the invention, e.g. compositions I of Example 1 and VII ofExample 5, and the isoparaffinic solvent extended post emulsifiable dyepenetrant compositions of the invention, e.g. composition IV of Example4, following emulsification thereof, also can be removed from a partsurface by washing with isopropyl alcohol or trichlorothane instead ofwith water.

All of the isoparaffinic solvent diluted formulations of the examplesappeared stable and no odor therefrom was detected. Washability of thewater-washable diluted dye penetrants from the parts was excellent, yetno overwashing of penetrant from the defects or cracks in the testsamples occurred during the tests.

From the foregoing, it is seen that the invention provides a highlyeffective water washable, solvent removable or post emulsifiable dyepenetrant composition consisting essentially of a nonionic surfactantand a dye, which is preferably fluorescent, and including a uniqueextender in the form of a specific essentially isoparaffinic solvent.Application of such isoparaffinic solvent extended dye penetrantcompositions to a part surface for detection of cracks therein resultsin efficiently and quickly obtaining fluorescent or visible lightindications of cracks in the part surface, equivalent in this respect tothe results obtained employing the same basic dye penetrant but in theabsence of the isoparaffinic solvent extender.

Since various changes and modifications of the invention will occur toand can be made readily by those skilled in the art without departingfrom the invention concept, the invention is not to be taken as limitedexcept by the scope of the appended claims.

I claim:
 1. A method for detecting cracks and other defects in thesurface of an object which comprises applying to said surface a liquiddye penetrant composition comprising (1) a nonionic surfactant, (2) asmall amount of a dye soluble in said surfactant and (3) as extender, asubstantial portion of an isoparaffinic solvent consisting essentiallyentirely of a mixture of isoparaffins having carbon chains ranging fromabout 10 to about 17 carbon atoms and an average carbon chain rangingfrom about 12 to about 15 carbon atoms, said isoparaffinic solvent beingpresent in an amount ranging from about 0.5 to 15 parts, to 1 part ofthe sum of said surfactant and said dye, by volume, removing excess dyepenetrant composition from said cracks and defects in said surface, andviewing the surface of said object under lighting conditions to obtaincolored traces from the dye in said cracks and other defects.
 2. Themethod as defined in claim 1, said isoparaffinic solvent having anaverage carbon chain ranging from about 13 to about 14 carbon atoms, andhaving a flash point of about 175° F. and an autoignition temperature ofabout 730° F.
 3. The method as defined in claim 1, said nonionicsurfactant being an oxyalkylated aliphatic alcohol or mixtures thereof,formed of an aliphatic primary or secondary alcohol carrying ethoxy orpropoxy groups, or mixtures thereof.
 4. The method as defined in claim3, said nonionic surfactant being of the group consisting of (a)straight chain, primary, aliphatic oxyalkylated alcohols, wherein saidalcohols can contain from 8 to 20 carbon atoms and the oxyalkyl groupsare ethylene oxide, propylene oxide, or a mixture of ethylene oxide andpropylene oxide groups, and (b) ethoxylates of linear secondaryaliphatic alcohols, with the hydroxyl groups randomly distributed, thelinear aliphatic portion of said alcohols being a mixture of alkylchains containing in the range from 10 to 17 carbon atoms, andcontaining an average of from 3 to 12 moles of ethylene oxide.
 5. Themethod as defined in claim 4, wherein said dye is a fluorescent dye andsaid dye is present in said composition in an amount ranging from about0.1 to 15 parts, per 100 parts, by weight of said surfactant, saidisoparaffinic solvent being present in an amount ranging from about 1 to7 parts, to 1 part of the sum of said surfactant and said dye, byvolume.
 6. The method as defined in claim 3, wherein said surfactantconsists of ethoxylates of a mixture of alcohols having the formula:##STR3## where n is in the range of from 9 to 13 and m is an average of3 to
 12. 7. The method as defined in claim 3, wherein said dye is afluorescent dye, and said surface of said object is viewed underfluoroescigenous light to obtain colored fluorescent traces from the dyein said cracks and other defects.
 8. The method as defined in claim 3,said isoparafinic solvent being present in an amount ranging from about0.5 to 15 parts, to 1 part of the sum of said surfactant and said dye,by volume.
 9. The method as defined in claim 3, said dye penetrantcomposition being a post emulsifiable dye penetrant composition whereinsaid surfactant in said post emulsifiable dye penetrant composition haslimited water solubility, including contacting the dye penetrant coveredsurface after application of said post emulsifiable dye penetrantcomposition, with an emulsifier containing as essential componenet asecond nonionic surfactant as above defined, said second surfactantbeing essentially water soluble, and contacting the emulsified penetranton the surface of said object with water or an organic solvent forremoving said emulsified dye penetrant from the surface of said object,and drying said surface prior to said viewing said object.
 10. Themethod as defined in claim 9, wherein said dye is a fluorescent dye andsaid dye is present in said dye penetrant composition in an amountranging from about 0.1 to 15 parts per 100 parts, by weight of saidsurfactant.
 11. The method as defined in claim 10, wherein saidsurfactant in both said dye penetrant composition and said emulsifierconsists of ethoxylates of a mixture of alcohols having the formula:##STR4## where n is in the range of from 9 to 13 and m is an average of3 to 12, and wherein m of said surfactant in said dye penetrantcomposition is an average of 3 to 4, and wherein m of said surfactant insaid emulsifier is an average of about 5 to
 12. 12. The method asdefined in claim 11, said isoparafinic solvent being present in anamount ranging from about 1 to 7 parts, to 1 part of the sum of saidsurfactant and said dye, by volume.
 13. The method as defined in claim1, including applying a developer to said surface after removing saidexcess dye penetrant composition from said surface, and prior to saidviewing the surface of said object.
 14. A liquid dye penetrantcomposition for use in nondestructive testing for detecting cracks andother defects in the surface of an object, comprising (1) a nonionicsurfactant, (2) a small amount of a dye soluble in said surfactant and(3) as extender, a substantial portion of an isoparaffinic solventconsisting of an isoparaffin having a carbon chain ranging from about 10to about 17 carbon atoms, said isoparaffinic solvent being present in anamount ranging from about 0.5 to 15 parts, to 1 part of the sum of saidsurfactant and said dye, by volume.
 15. A liquid dye penetrantcomposition for use in nondestructive testing for detecting cracks andother defects in the surface of an object, comprising (1) a nonionicsurfactant, (2) a small amount of a dye soluble in said surfactant and(3) as extender, a substantial portion of an isoparaffinic solventconsisting essentially entirely of a mixture of isoparaffins havingcarbon chains ranging form about 10 to about 17 carbon atoms and averagecarbon chain ranging from about 12 to about 15 carbon atoms, saidisoparaffinic solvent being present in an amount ranging from about 0.5to 15 parts, to 1 part of the sum of said surfactant and said dye, byvolume.
 16. The dye penetrant composition as defined in claim 15, saidisoparaffinic solvent having an average carbon chain ranging from about13 to about 14 carbon atoms, and having a flash point of about 175° F.and an autoignition temperature of about 730° F.
 17. The dye penetrantcomposition as defined in claim 15, said nonionic, surfactant beingselected from the group consisting of oxyalkylated aliphatic alcohols,alkoxylated alkyl phenols and alkyl aryl polyether alcohols, andmixtures thereof.
 18. The dye penetrant composition as defined in claim15, said nonionic surfactant being an oxyalkylated aliphatic alcohol ormixtures thereof, formed of an aliphatic primary or secondary alcoholcarrying ethoxy or propoxy groups, or mixtures thereof.
 19. The dyepenetrant composition as defined in claim 18, wherein said surfactantconsists of the ethoxylates of a mixture of C₁₂ to C₁₅ linear primaryalcohols and contains from 5 to 9 moles of ethylene oxide per mole ofprimary alcohol.
 20. The dye penetrant composition as defined in claim15, said nonionic surfactant being of the group consisting of (a)straight chain, primary, aliphatic oxyalkylated alcohols, wherein saidalcohols can contain from 8 to 20 carbon atoms and the oxyalkyl groupsare ethylene oxide, propylene oxide, or a mixture of ethylene oxide andpropylene oxide groups, and (b) ethoxylates of linear secondaryaliphatic alcohols, with the hydroxyl groups randomly distributed, thelinear aliphatic portion of said alcohols being a mixture of alkylchains containing in the range from 10 to 17 carbon atoms, andcontaining an average of from 3 to 12 moles of ethylene oxide.
 21. Thedye penetrant composition as defined in claim 20, wherein said nonionicsurfactant in the dye penetrant composition is the sole liquid carrierfor the dye therein.
 22. The dye penetrant composition as defined inclaim 20, wherein said surfactant (a) is a mixture of compounds havingthe formula:

    R--O(A)H

wherein R is an essentially linear alkyl group having from 10 to 18carbon atoms, at least 70 weight percent of said compounds in saidmixture having an R of from 12 to 16 carbon atoms, and A is a mixture ofoxypropylene and oxyethylene groups, said oxypropylene and oxyethylenegroups being from 55 to 80% of the total weight of said compounds, theoxypropylene to oxyethylene ratio of said total weight being from 0.85:1to 2.75:1; and wherein said surfactant (b) are ethoxylates of a mixtureof alcohols having the formula: ##STR5## where n is in the range from 9to 13 and m is an average of 3 to 12; and said dye is present in saidcomposition in an amount ranging from about 0.1 to 15 parts, per 100parts, by weight, of said surfactant.
 23. The dye penetrant compositionas defined in claim 22, wherein R in said surfactant (a) can have from12 to 18 carbon atoms, and the total number of A groups can range fromabout 4 to about 14; and wherein in said surfactant (b) the linear alkylhydrophobic portion of said surfactant is a polyoxyethylene chainrandomly attached to the linear alkyl hydrophobic chains through anether linkage, and wherein said surfactant (b) is selected from thegroup consisting of said ethoxylates of said mixture of alcohols,wherein n ranges from 9 to 13, and m is an average of 3, 5, 7, 9 or 12.24. The dye penetrant composition as defined in claim 15, wherein saiddye is a fluorescent dye.
 25. The dye penetrant composition as definedin claim 15, wherein said surfactant consists of ethoxylates of amixture of alcohols having the formula: ##STR6## where n is in the rangefrom 9 to 13 and m is an average of 3 to
 12. 26. The dye penetrantcomposition as defined in claim 25, wherein said surfactant is selectedfrom the group consisting of said ethoxylates of said mixture ofalcohols, wherein n ranges from 9 to 13, and m is an average of 3, 5, 7,9, or
 12. 27. The dye penetrant composition as defined in claim 25,wherein said dye is a fluorescent dye, said solvent being present in atleast equal volumetric proportions with respect to said surfactant. 28.The dye penetrant composition as defined in claim 25, employing acombination of said nonionic surfactants wherein m is one of saidsurfactants is an average of 5 and m in another of said surfactants isan average of
 9. 29. The dye penetrant composition as defined in claim25, said isoparaffinic solvent having an average carbon chain rangingfrom about 13 to about 14 carbon atoms, and having a flash point ofabout 175° F. and an autoignition temperature of about 730° F., and anaverage molecular weight of
 191. 30. The dye penetrant composition asdefined in claim 15, said isoparaffinic solvent being present in anamount ranging from about 1 to 7 parts, to 1 part of the sum of saidsurfactant and said dye, by volume.